It is narrated from Sayyiduna Abdullah bin Aqram (may Allah be pleased with him) that he was with his father in the plain of Namirah. A caravan passed by us and they made their camels kneel at the side of the road. He said to me: My son, stay with our animals until I go near these riders. He went near them and I went near with him. Then the prayer was established, and there was the Messenger of Allah (peace and blessings be upon him) among them. So I kept looking at the whiteness of the armpits of the Messenger of Allah (peace and blessings be upon him) every time he prostrated.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14064